The present invention relates to new and improved resin compositions and more particularly to thermoplastic resin compositions such as polyolefines, polyvinylchloride and polyamide, and to a method for the production of resin compositions. The invention further relates to a filler blend for use in the production of resin compositions.
It is well known to produce polyolefines such as polypropylene compound containing functional fillers such as fine particulate talc to increase the stiffness of the final polypropylene product.
Talc is hydrated magnesium silicate with the theoretical formula 3MgO.4SiO4.H2O and consists of magnesiumhydroxide sandwiched between two sheets of silica.
When adding other fillers in addition to talc in order to improve other properties, such as for example impact strength, it has, however, been found that the stiffness obtained by using talc alone as a filler is substantially reduced when adding a second filler for increasing the impact strength. It has therefore not been possible to produce polypropylene products with both a high stiffness and a high impact strength. High stiffness and high impact strength is particularly important in some polypropylene products such as for example car bumpers. The same is true for other thermoplastic resin products.
The term thermoplastic resin used in the specification and claims includes not only thermoplastic resins per se, but also mixtures thereof, as well as a blend of thermoplastic resins with other materials such as an elastomer like nitrile rubber. The so-called thermoplastic rubbers, thermoplastic elastomers are also included in the definition of thermoplastic resin. Thermoplastic resins per se includes polyolefines, polystyrene, polyesters, ABS copylymers, polyvinyl chloride (PVC), unplasticized polyvinyl chloride (UPVC), polyamide, acrylic polymers, polycarbonate polymers, polysulfone polymers and others.
It is known from U.S. Pat. No. 4,722,952 that the addition of microsilica to polyvinylchloride, improves the impact strength of polyvinylchloride used for the production of electrical conduits. For such products the stiffness is of no importance. On the contrary, high stiffness is not desired for electrical conduits.
The term microsilica used in the specification and claims is particulate amorphous SiO2 obtained from a process in which silica is reduced and the reduction product is oxidized in vapor phase to form amorphous silica. Microsilica may contain at least 70% by weight silica (SiO2) and have a specific density of 2,1-2.3 g/cm3 and a surface area at 15-30 m2/g. The primary particles are substantially spherical. The primary particles have an average size of about 0,15 xcexcm. Microsilica is preferably obtained as a co-product in the production of silicon or silicon alloys in electric reduction furnaces. In these processes large quantities of silica are formed as SiO2. The SiO2 is recovered in conventional manner using filter or other collection apparatus. For the purpose of the present invention the term microsilica also shall be understood to include fly-ash, and more particularly fly-ash particles of substantial spherical shape having a particle size below 10 microns.